1. Field of the Invention
The application relates to a method utilized in a wireless communication system and a communication device thereof, and more particularly, to a method of HARQ entity handling in a wireless communication system and a related communication device.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B (NB) alone rather than in NB and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
Architecture of the radio interface protocol of a LTE system includes three layers: the Physical Layer (Layer 1), the Data Link Layer (Layer 2), and the Network Layer (Layer 3), where a control plane of Layer 3 is a Radio Resource Control (RRC) layer, and Layer 2 is further divided into a Packet Data Convergence Protocol (PDCP) layer, a Radio Link Control (RLC) layer and a Medium Access Control (MAC) layer.
There is a MAC entity in the MAC layer of a user equipment (UE) for handling transport channels, such as broadcast channel (BCH), downlink shared channel (DL-SCH), paging channel (PCH), uplink shared channel (UL-SCH), random access channel (RACH), and multicast channel (MCH). In addition, if a reset of the MAC entity is requested by upper layers (e.g. the RRC layer), the UE shall stop (if running) all MAC timers, consider the time alignment timer as expired, set the new data indicators (NDIs) for all uplink HARQ processes to a default value (e.g. 0) for a new transmission, stop ongoing random access procedure, cancel triggered scheduling request procedure, cancel triggered buffer status reporting procedure, cancel triggered power headroom reporting procedure, flush soft buffers for all downlink HARQ processes, for each downlink HARQ process, consider the next received transmission for a transport block (TB) as the very first transmission, release temporary cell radio network temporary identifier (C-RNTI).
Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced system is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced system targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO), etc.
For bandwidth extension, carrier aggregation is introduced to the LTE-Advanced system for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths (for example up to 100 MHz) and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, where the UE can establish multiple links corresponding to the multiple component carriers for simultaneously receiving and transmitting. In carrier aggregation, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the NAS mobility information, and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as a Primary Cell (PCell). In the downlink, the component carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC). In addition, for both uplink and downlink, each component carrier includes a HARQ entity, which maintains a number of parallel HARQ processes allowing transmissions to take place continuously while waiting for the feedback (acknowledgement (ACK) or non-acknowledgement (NACK)) on the successful or unsuccessful reception of previous transmissions.
For a UE supporting a single component carrier in the LTE system, a NDI of a HARQ entity is set to a default value when the MAC entity is reset. For a UE supporting multiple component carriers in the LTE-Advanced system, there is no clear specification for HARQ entity reset. More specifically, how to set a new data indicator for an uplink HARQ process of the HARQ entity is not defined. When a component carrier configuration of the UE is changed (e.g. a component carrier is reconfigured, added, or removed by RRC layer, or is activated or deactivated by MAC layer), the UE may reset all HARQ entities in multiple component carriers based on the MAC entity reset mechanism. This makes data transmission failed. For example, since only the component carrier is reconfigured, added, removed, activated, or deactivated, the UE sets new data indicators for all HARQ processes in all HARQ entities to a default value (e.g. 0) for a new transmission. Thus, new data indicators for other component carriers may be set differently between the UE and an eNB. Therefore, the UE transmits a retransmission but actually the eNB schedules as a new transmission, causing data transmission failure.